Local variable tracking: emit, decode, and render values in the tracer#270
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Local variable tracking: emit, decode, and render values in the tracer#270gnidan wants to merge 3 commits into
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Emit a `variables` context at each instruction naming the in-scope
locals and, for each, a pointer to the memory word holding its current
value — a per-instruction snapshot the tracer resolves and decodes.
A sub-word scalar (address, bool, intN/uintN, bytesN) is homed by a
full-word MSTORE, so its value occupies the whole 32-byte word. Name the
full word and let the type-directed decoder extract the meaningful bytes,
rather than the type's narrow byte width at the word start — which, for a
right-aligned value, is the zero padding, so an address or bool would
otherwise resolve to zero. uint256 was already correct (its width is a
full word).
Attach the pointer only when the local solely occupies its word: the
allocator byte-packs several sub-word scalars into one word and their
full-word stores clobber each other, so a packed sub-word local has no
recoverable value — it is emitted type-only ("in scope, no value") until
codegen stops byte-packing sub-word scalars.
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Resolve each local to the pointer region holding its current value rather than every region it has occupied, narrow the trace drawer's local rendering to that region, and decode the resolved bytes to a typed value (replacing the raw formatAsDecimal fallback). Add an address round-trip trace-playground example (`idn(owner: address)`) so a decoded, EIP-55-checksummed non-uint value is visible when stepping into the call.
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This PR adds end-to-end local-variable value tracking to the tracer, from
compiler emission through decoding to the rendered value in the drawer. It
reassembles three pieces the team is reviewing as one coherent change.
Format / packages
pointers: add a scalar-first, type-directed value decoder — resolves aregion's bytes to a typed value (uint, EIP-55-checksummed address, bool,
intN, bytesN).
bugc: emit a sound per-instruction local-variable debug snapshot —variablescontexts naming each in-scope local and a pointer to thememory word holding its current value. A sub-word scalar points at its
full 32-byte word (the decoder type-aligns within it), gated on sole
occupancy: a byte-packed sub-word local carries no recoverable value and
lists as type-only rather than a wrong one.
Implementation
web/programs-react: resolve each local to the region holding itscurrent value (not every region it has occupied), narrow the trace
drawer's rendering to that region, and decode the resolved bytes to a
typed value. Adds an address round-trip trace-playground example so a
decoded, checksummed address is visible when stepping into the call.
Together these render a local's live value as a single decoded value that
persists across the call, rather than a raw region dump.
Scope (O0): a value pointer is emitted for frame-spilled values —
parameters and memory-homed locals. A
letthat stays stack-resident hasno memory home, so it lists as type-only ("in scope, no value") regardless
of occupancy — intended at O0, not a gap.